JavaScript Array concat() Method

The Array.concat() method is a built-in JavaScript function that merges two or more arrays or values into a new array. It does not modify the original arrays but returns a new array containing the elements of the input arrays and any additional values.

Syntax

arr.concat(value1, value2, ..., valueN);

Parameters

Parameter	Description
value1, ..., valueN	Arrays or values to concatenate with the original array. These can include any data type.

Return Value

The concat() method returns a new array that combines the elements of the original array with the specified arrays or values.

Example 1: Concatenating Two Arrays

let arr1 = [10, 20, 30];
let arr2 = [40, 50, 60];

let result = arr1.concat(arr2);
console.log(result); 
// Output: [10, 20, 30, 40, 50, 60]

Example 2: Concatenating Multiple Arrays

let arr1 = [10];
let arr2 = [20, 30];
let arr3 = [40, 50, 60];

let result = arr1.concat(arr2, arr3);
console.log(result); 
// Output: [10, 20, 30, 40, 50, 60]

Example 3: Adding Primitive Values

let arr = [10, 20, 30];

let result = arr.concat(40, 50);
console.log(result); 
// Output: [10, 20, 30, 40, 50]

Example 4: Concatenating Nested Arrays

let arr1 = [1, 2];
let arr2 = [[3, 4]];

let result = arr1.concat(arr2);
console.log(result); 
// Output: [1, 2, [3, 4]]

Example 5: Concatenating Empty Arrays – Concatenating an empty array does not affect the original array.

let arr1 = [10, 20, 30];
let arr2 = [];

let result = arr1.concat(arr2);
console.log(result); 
// Output: [10, 20, 30]

Example 6: Concatenating Objects – Objects can also be concatenated into the resulting array.

let arr1 = [1, 2];
let obj = { key: 'value' };

let result = arr1.concat(obj);
console.log(result); // Output: [1, 2, { key: 'value' }]

Example 7: Using concat() with Strings

let str1 = ['Hello'];
let str2 = ['World'];

let result = str1.concat(str2);
console.log(result); 
// Output: ['Hello', 'World']

Supported Browsers

Browser	Support
Chrome	1+
Firefox	1+
Safari	1+
Edge	12+
Opera	4+
Internet Explorer	5.5+

Note: Large Arrays – Concatenating extremely large arrays may affect performance due to memory and computation overhead.